This invention relates to an anode substrate for a display device which includes a glass plate provided on an inner surface thereof with color filters and a method for manufacturing the same, and more particularly to a color filter-equipped anode substrate for a display device such as, for example, a fluorescent display device, a field emission display (FED) utilizing field emission cathodes (FECs) as an electron source, a plasma display (PDP) or the like and a method for manufacturing the same.
There has been known in the art a color fluorescent display device including a combination of a phosphor ZnO:Zn emitting light of a bluish green luminous color and color filters. Manufacturing of the color fluorescent display device includes a heat treatment step carried out at a temperature of 500.degree. C., thus, a material for the color filters is required to be heat resistant. For example, color filters made of an organic material and used for an LCD or the like fail to be used for the color fluorescent display device. Thus, it is required to make the color filters of an inorganic material. Inorganic materials conventionally used for this purpose include a metal colloid, an inorganic pigment and the like.
Now, arrangement of color filters in an FED will be described with reference to FIG. 6. First of all, an anode substrate 100 made of a light-permeable material such as glass or the like is formed thereon with color filters 101, 102 and 103, on which a smoothing layer 104 is commonly arranged. Then, transparent conductive films 105 made of indium tin oxide (ITO) or the like are arranged on the smoothing layer 104. The smoothing layer 104 may be constituted of a SiO.sub.2 film or the like made by sputtering, vapor deposition, CVD, sol-gel techniques or the like. Then, a phosphor is deposited on each of the transparent conductive films 105, to thereby form a phosphor layer, resulting in the anode substrate 100 being finished. Then, a cathode substrate on which FECs are formed is arranged in such a manner that the FECs face the phosphors of the anode substrate 100 while being spaced at a microdistance from the phosphors. Finally, both substrates are sealedly joined to each other by means of a spacer member arranged in a gap defined therebetween while being positioned at an outer periphery of the substrates, to thereby provide an envelope, which is then evacuated to a high vacuum.
In operation of the thus-formed FED, electrons emitted from the FECs are impinged on the phosphor layers of the anode substrate 100, leading to luminescence of the phosphor layers. Luminescence of the phosphor layers is observed through the transparent conductive films 105, color filters 101, 102 and 103, and anode substrate 100 from an outside of the anode substrate 100. The ZnO:Zn phosphor has a wide spectrum. Thus, when the color filters 101, 102 and 103 are colored red (R), green (G) and blue (B) and the phosphor layers are selectively driven so as to emit light in a dot-like manner, the FED is permitted to carry out full-color graphic display.
A color filter made of an inorganic material is disclosed in Japanese Patent Application Laid-Open Publication No. 310061/1994 and Japanese Patent Application Laid-Open Publication No. 73827/1995. Unlike an organic color filter, the inorganic color filter is reduced in tinting strength. Thus, in order to ensure that the inorganic color filter satisfactorily exhibits a color reproduction range, it is required that the color filter is formed into an increased thickness as large as several microns to tens of microns. Unfortunately, such an increase in thickness of the color filter causes a difference in level to occur between the color filter and the anode substrate. This requires to laminatedly arrange the smoothing layer on the color filters to smooth an upper surface of the color filters as described above. However, there has been found no inorganic material which permits the smoothing layer increased in thickness in conformity to the color filters to be provided at a reduced cost. Thus, formation of the smoothing layer sufficiently increased in thickness in conformity to a thickness of the color filters so as to prevent formation of the difference in level causes the smoothing layer 104 to be readily broken or cracked. In view of such a problem, it would be considered that the transparent conductive films 105 each are formed directly on each of the color filters 101, 102 and 103 as shown in FIG. 7. Unfortunately, this causes disconnection of the transparent conductive film 105 at a level difference between each of the color filters 101, 102 and 103 and the anode substrate 100. Also, such formation of the smoothing layer 104 on the color filters using SiO.sub.2 or the like as described above with reference to FIG. 6 actually renders smoothing of the level difference between the color filters 101, 102 and 103 and the anode substrate 100 highly difficult as shown in FIG. 8, so that the level difference leads to disconnection of the transparent conductive film 105 of ITO or the like formed on each of the color filters 101, 102 and 103. Further, this, even when such disconnection of the transparent conductive films 105 does not occur, gives rise to another problem when the phosphor layers are formed on the transparent conductive films 105 by rotary coating in the subsequent step. More particularly, the rotary coating includes a step of rotating the substrate to spread a liquid for forming each of the phosphor layers on the substrate by centrifugal force, leading to formation of a film of the phosphor forming liquid. However, this substantially fails to permit the phosphor forming liquid which run onto the level difference on the substrate by centrifugal force to be uniformly coated all over each of the transparent conductive films 105, to thereby render the coating non-uniform.